The present invention relates to a brake fluid pressure generating device which generates brake fluid pressure via a control valve in response to operation of a brake operating means such as a brake pedal and, more particularly, to a brake fluid pressure generating device which can prevent the operating stroke of the brake operating means from being varied even with variation in consumption of brake fluid by that brake fluid pressure control is conducted regardless of the operation of the brake operating means on a wheel cylinder side of the brake fluid pressure generating device.
For example, in a conventional brake system of an automobile, a brake fluid pressure generating device has been employed which boosts a pedaling force exerted on a brake pedal by fluid pressure into predetermined magnitude to develop large brake fluid pressure. The brake fluid pressure generating device functions to provide a large braking force from a small pedaling force exerted on the brake pedal, thereby securing the braking action and reducing the fatigue of a driver.
Such conventional brake fluid pressure generating device can be roughly classified into the following types: one employing a vacuum booster for boosting the pedaling force by negative pressure to actuate the master cylinder, one employing a hydraulic booster for boosting the pedaling force by fluid pressure to actuate the master cylinder, one used in a full-power brake system for directly supplying fluid pressure to wheel cylinders, and the other one employing a pneumatic booster or an electromagnetic booster for boosting the pedaling force by compressed air or electromagnetic force to actuate a master cylinder.
FIG. 13 is a schematic illustration of a brake system with a brake fluid pressure generating device employing a conventional vacuum booster and FIG. 14 is a schematic illustration of a brake system employing a conventional hydraulic booster. In the following description of the prior art and description of embodiments, terms such as xe2x80x9ctopxe2x80x9d, xe2x80x9cbottomxe2x80x9d, xe2x80x9cright-handxe2x80x9d, xe2x80x9cleft-handxe2x80x9d describe and correspond to the top, the bottom, the right-hand, and the left-hand in the associated drawings, and terms xe2x80x9cfrontxe2x80x9d and xe2x80x9crearxe2x80x9d correspond to the left and the right in the associated drawings.
In the brake system with the brake fluid pressure generating device employing the vacuum booster shown in FIG. 13, an input force F1 is exerted to an input shaft 4 of the brake fluid pressure generating device 1 by depression of a brake pedal 3 as a brake operating means so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is isolated from a low-pressure (L) valve passage 5b1 of a second valve element 5b connected to a negative pressure source and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to the atmospheric air. The atmospheric air is controlled according to the input F1 by the control valve 5 to develop control valve output pressure Pr. The control valve output pressure Pr is supplied to a power chamber 15b of the power cylinder unit 15 so that a power piston 15a moves to the left to produce output Fp which is a boosted pedaling force. A master cylinder piston 16a is actuated by the output Fp so that a master cylinder 16 generates master cylinder pressure Pm which is supplied to wheel cylinder(s) 9 as braking fluid pressure Pb, thereby actuating the brake. A reaction force Fm from the master cylinder 16 is modulated as a reaction force Fv by a reaction mechanism 57 and is applied to the first valve element 5a. Therefore, the control valve output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force F1 of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3. In the vacuum booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 15a. 
In the break system with the brake fluid pressure generating device employing the hydraulic booster shown in FIG. 14, an input force F1 is exerted to an input shaft 4 by depression of a brake pedal 3 so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is isolated from a low-pressure (L) valve passage 5bl of a second valve element 5b connected to a reservoir and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to a fluid pressure source. The hydraulic pressure of the fluid pressure source such as a pump and an accumulator is controlled according to the input F1 by the control valve 5 to generate control valve output pressure Pr. The control valve output pressure Pr is supplied to a power chamber 15b of the power cylinder unit 15 so that a power piston 15a moves to the left to produce output Fp which is a boosted pedaling force. A master cylinder piston 16a is actuated by the output Fp so that a master cylinder 16 generates master cylinder pressure Pm which is supplied to wheel cylinder(s) 9 as braking fluid pressure Pb, thereby actuating the brake. A reaction force Fm from the master cylinder 16 and a reaction force by the control valve output pressure Pr of the control valve 5 are modulated as a reaction force Fv by a reaction mechanism 57 and is applied to the first valve element 5a. Therefore, the control valve output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force F1 of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3. In the hydraulic booster, in the same manner as the vacuum booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 15a. 
By the way, such conventional brake systems employ various brake controls such as for controlling the braking force during the braking action, for example, Brake Assist Control for increasing the braking force when the braking force is insufficient for emergency brake or the like, and Regenerative Brake Coordination Control to be performed when a regenerative brake system is used to generate braking pressure during the braking action by the service brake system, and Automatic Brake Controls, for example, a brake control for controlling the distance from a vehicle in front, a brake control for avoiding a collision with an obstacle object, and Traction Control (TRC).
Most of such brake controls are normally conducted in a brake circuit between the master cylinder 16 and the wheel cylinder(s) 9. However, when the brake control is conducted in the brake circuit after the master cylinder, it is required to prevent the pedal stroke of or pedaling force on the brake pedal 3 from being affected by such brake controls, for instance, for obtaining better operational feeling.
However, in the aforementioned conventional brake systems, the stroke of the master cylinder piston 16a is defined by the relation between the master cylinder 16 and the wheel cylinder(s) 9. Accordingly, the stroke of the input shaft 4 of the brake fluid pressure generating device 1, i.e. the pedal stroke of the brake pedal 3, depends on the stroke of the master cylinder piston 16a. That is, the stroke for input is affected by the brake controls conducted in the brake circuit after the master cylinder 16. In the brake system employing the conventional brake fluid pressure generating device 1, it is hard to securely and sufficiently satisfy the aforementioned requirement.
If the input side and the output side are just separated from each other to produce outputs regardless of the stroke of the input side, the input side does not travel so that the stroke of the input side can not be ensured.
For this, a full power brake system has been conventionally proposed in which a stroke simulator is provided on the brake circuit after the master cylinder 16 to prevent the stroke of the input side from being affected by the brake control after the master cylinder and to ensure the stroke of the input side.
In this type of full power brake system shown in FIG. 15, an input force F1 is exerted to an input shaft 4 by depression of a brake pedal 3 so that the input shaft 4 moves in the operative direction. Then, a first valve element 5a of a control valve 5 moves to the left so that an output port 5c of the first valve element 5a is isolated from a low-pressure (L) valve passage 5b1 of a second valve element 5b connected to a reservoir and is connected to a high-pressure (H) valve passage 5b2 of the second valve element 5b connected to a fluid pressure source. The hydraulic pressure of the fluid pressure source such as a pump and an accumulator is controlled according to the input F1 by the control valve 5 to generate control valve output pressure Pr. The control valve output pressure Pr is supplied to wheel cylinder(s) 9 as braking fluid pressure Pb, thereby actuating the brake.
At the same time, the control valve output pressure Pr is also supplied to a power chamber 15b of the power cylinder unit 15 so that the power piston 15a moves to the left to produce output Fp. The master cylinder piston 16a is actuated by the output Fp so that the master cylinder 16 generates master cylinder pressure Pm which is supplied to the stroke simulator 58 whereby a piston of the stroke simulator 58 moves to the left, thereby ensuring the stroke of the input shaft 4, i.e. the stroke of the first valve element 5a. A reaction force Fm from the master cylinder 16 and a reaction force by the control valve output pressure Pr of the control valve 5 are modulated as a reaction force Fv by a reaction mechanism 57 and is applied to the first valve element 5a. Therefore, the control valve output pressure Pr of the control valve 5 is regulated to balance the reaction force Fv with the input force F1 of the input shaft 4. The reaction force Fv is transmitted to a driver through the input shaft 4 and the brake pedal 3.
In the control valve 5 of the full power brake system, in the same manner as the vacuum or hydraulic booster, the first valve element 5a moves together with the input shaft 4 and the second valve element 5b moves together with the power piston 15a. 
However, to prepare the additional stroke simulator 58, many parts (of which some parts are not shown) such as a stroke cylinder and an electromagnetic switching valve used for the stroke simulator 58 are required, making the structure complex and increasing the cost.
In a regenerative coordination brake system composed of a combination of a service brake system and a regenerative brake system, when the regenerative brake system is actuated during service braking by the operation of the brake fluid pressure generating device, the braking force produced by the brake fluid pressure generating device 1 should be reduced for the braking force produced by the regenerative brake system. In this case, it is desired to conduct the control of the brake fluid pressure on the wheel cylinder side.
In a brake system composed of a combination of a service brake system and a brake assist system, it is desired to increase the output of the brake fluid pressure generating device to intensify the braking force produced by the brake fluid pressure generating device in such case that brake assist operation is needed, for example, a case that a driver can not depress a brake pedal enough during the operation of the brake fluid pressure generating device 1 so as not to produce a predetermined braking force. In this case also, it is desired to conduct the control of the brake fluid pressure on the wheel cylinder side.
As mentioned above, since the consumption of brake fluid by the control of the braking pressure varies when the control of the braking pressure is conducted on the wheel cylinder side independently from the operation of the brake pedal during the service braking operation, the pedal stroke is affected in the conventional brake fluid pressure generating device 1. That is, in the conventional brake fluid pressure generating device 1, desired pedal stroke can not be obtained because it is affected by variation in consumption of the brake fluid.
It is an object of the present invention to provide a brake fluid pressure generating device which can provide a desired operation stroke characteristic of a brake operating means regardless of variation in consumption of brake fluid in a brake circuit.
To achieve the aforementioned objects, the present invention provides a brake fluid pressure generating device. A brake fluid pressure generating device comprises at least an input shaft which is actuated by input applied through the operation of a brake operating means, and a control valve which is operated by the input of said input shaft to regulate the pressure of a pressure source according to the operational input (operational stroke, operational force) of the said brake operating means to output regulated control valve output pressure, wherein said control valve has a first valve element and a second valve element which are movable relative to each other, said first valve element is subjected to the input of said input shaft and a first force relating to said input which counteract with each other, and said second valve element is subjected to a second force relating to said input and a second valve element converted force which is produced by converting the stroke of the second valve element by a first converting factor which counteract with each other, and said first valve element is controlled to balance said input and said first force and said second valve element is controlled to balance said second force and said second valve element converted force, whereby the control valve output pressure regulated according to the operational input of said brake operating means is generated.
The present invention is characterized in that said second force applied to said second valve element is a first control valve converted force which is produced by converting said control valve output pressure by a second converting factor, or a component of the force corresponding to the operational input of said brake operating means which is produced by distributing the force according to a first distribution factor.
The present invention is further characterized in that said first force applied to said first valve element is a first valve element converted force which is produced by converting the stroke of said first valve element by a third converting factor, or a second control valve converted force which is produced by converting said control valve output pressure by a forth converting factor.
Further, the present invention is characterized by further comprising a power cylinder unit in which said control valve output pressure is supplied and a power piston is moved by the supplied control valve output pressure so as to output, and a master cylinder which is actuated by the output of said power cylinder unit to generate master cylinder pressure, wherein said second force applied to said second valve element is a converted force which is produced by converting the stroke of said power piston by a fifth converting factor, a first control valve converted force which is produced by converting said control valve output pressure by a second converting factor, or a component of the force corresponding to the operational input of said brake operating means which is produced by distributing the force according to a first distribution factor.
Furthermore, the present invention is characterized in that said first force applied to said first valve element is a first valve element converted force which is produced by converting the stroke of said first valve element by a third converting factor, a second control valve converted force which is produced by converting said control valve output pressure by a forth converting factor, or a master cylinder converted force which is produced by converting said master cylinder pressure by a sixth converting factor.
Moreover, the present invention is characterized in that an assist biasing force for shifting said first valve element relative to said second valve element is applied between said first and second valve elements, wherein said first valve element is controlled to balance said input, said first force, and said assist biasing force, and said second valve element is controlled to balance said second force, said second valve element converted force, and said assist biasing force, whereby the control valve output pressure regulated according to the operational input of said brake operating means is generated.
In addition, the present invention is characterized in that said assist biasing force is an electromagnetic force by a solenoid coil.
The present invention is further characterized in that the input of said input shaft applied to said first valve element is a component of the force corresponding to the operational input of said brake operating means which is produced by distributing the force according to a second distribution factor.
In the brake fluid pressure generating device of the present invention having the aforementioned structure, the input side and the output side are separated from each other, whereby stroke of a brake operating means can be prevented from being varied even when braking pressure control is conducted in a brake circuit on the brake cylinder side after a control valve independently of the input of the input side during normal braking operation so that the consumption of brake fluid is varied.
The device can provide desired stroke characteristic of the brake operating means without being affected by variation in consumption of brake fluid on the output side of the brake fluid pressure generating device.
Further, the device allows the braking force control in the brake circuit on the brake cylinder side after the control valve to be conducted independently of the input of the input side during normal braking operation. Therefore, the brake fluid pressure generating device of the present invention can be easily and flexibly adopted to a system which needs the control of braking pressure, for example, decreasing the braking pressure for regenerative brake coordination control of a regenerative brake coordination system and increasing the braking pressure for brake assist control of a brake assist system, independently of the operation of the brake operating means during operation of the brake fluid pressure generating device.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.